using System.Net;
using System.Net.Http.Headers;
using System.Net.Http.Json;
using System.Text.Json.Serialization;
using Acl.Application;

namespace Acl.Infrastructure;

/// <summary>
/// The only code that talks to the Objecten API (ADR-0028). Writes the register record as an object
/// of the <c>RegisterRecord</c> objecttype registered in S-18c.
/// </summary>
public sealed class ObjectenGateway(HttpClient http, ObjectenOptions options, IClock clock) : IRegisterRecordGateway
{
    // The objecttype URL + version are assigned by Objecttypen at seed time, so they are resolved by
    // name on first use rather than pinned in config (same reasoning as ADR-0021).
    // ponytail: memoised per instance only — the gateway is a transient typed client, so in practice
    // that is one extra GET per approval against a neighbouring container. Lift it into a singleton
    // cache (as CachedZaaktypeCatalog does for ZGW) if approvals ever get hot.
    private Objecttype? objecttype;

    public async Task UpsertAsync(RegisterRecord record, CancellationToken ct = default)
    {
        ArgumentNullException.ThrowIfNull(record);

        var type = objecttype ??= await ResolveObjecttypeAsync(ct);
        var existing = await FindExistingAsync(type.Url, record.Id, ct);
        var data = new RecordDataDto(record.Id, record.Status, record.Reference);

        // No existing object → create; otherwise PATCH, which appends a new record version to the same
        // object. Either way the register ends up with exactly one object per registration (§8.6).
        if (existing is null)
            await SendAsync(HttpMethod.Post, new Uri(options.BaseUrl, "/api/v2/objects"),
                new CreateObjectDto(type.Url.ToString(), NewRecord(type.Version, data)),
                "Creating the register record", ct);
        else
            await SendAsync(HttpMethod.Patch, existing,
                new PatchObjectDto(NewRecord(type.Version, data)),
                "Updating the register record", ct);
    }

    public async Task<RegisterRecord?> GetAsync(Uri objectUrl, CancellationToken ct = default)
    {
        ArgumentNullException.ThrowIfNull(objectUrl);

        // Fetched by the URL the notification carried, so no objecttype resolution and no search —
        // unlike a write, which has to find the object for a registration id.
        using var message = new HttpRequestMessage(HttpMethod.Get, objectUrl);
        message.Headers.Authorization = new AuthenticationHeaderValue("Token", options.Token);
        message.Headers.Add("Accept-Crs", "EPSG:4326");

        using var response = await http.SendAsync(message, ct);
        // The object may be gone by the time a (possibly redelivered) notification is handled —
        // there is simply nothing to project, which is not a failure (§8.6).
        if (response.StatusCode == HttpStatusCode.NotFound)
            return null;

        await EnsureSuccessAsync(response, "Reading the register record", ct);

        var body = await response.Content.ReadFromJsonAsync<ReadObjectDto>(ct)
            ?? throw new InvalidOperationException("Objecten returned an empty object response");
        var data = body.Record?.Data;
        return data is null ? null : new RegisterRecord(data.Id, data.Status, data.Reference);
    }

    private RecordDto NewRecord(int typeVersion, RecordDataDto data) =>
        new(typeVersion, data, clock.Today.ToString("yyyy-MM-dd"));

    /// <summary>The URL + latest published version of the configured objecttype, read from Objecttypen.</summary>
    private async Task<Objecttype> ResolveObjecttypeAsync(CancellationToken ct)
    {
        var page = await GetAsync<ObjecttypePage>(
            new Uri(options.ObjecttypenBaseUrl, "/api/v2/objecttypes"),
            options.ObjecttypenToken, crs: false, "objecttypen", ct);

        var match = (page.Results ?? []).FirstOrDefault(o => o.Name == options.ObjecttypeName)
            ?? throw new InvalidOperationException(
                $"No objecttype '{options.ObjecttypeName}' registered in Objecttypen — is the RegisterRecord seed applied?");

        // Write against the highest *published* version: a draft version's schema is still being
        // shaped, and objects written against it would be validated by a moving target. The objecttype
        // carries its versions as URLs, so each is fetched for its status (the collection response
        // gives no status) — once per gateway instance, alongside the lookup above.
        var latest = 0;
        foreach (var versionUrl in match.Versions ?? [])
        {
            var version = await GetAsync<ObjecttypeVersionDto>(
                new Uri(versionUrl), options.ObjecttypenToken, crs: false, "objecttype version", ct);
            if (version.Status == "published" && version.Version > latest)
                latest = version.Version;
        }

        if (latest == 0)
            throw new InvalidOperationException($"Objecttype '{options.ObjecttypeName}' has no published version");

        return new Objecttype(new Uri(match.Url), latest);
    }

    /// <summary>The URL of the object already holding this registration's record, or null if there is none.</summary>
    private async Task<Uri?> FindExistingAsync(Uri objecttypeUrl, string id, CancellationToken ct)
    {
        var query = new Uri(options.BaseUrl,
            "/api/v2/objects?type=" + Uri.EscapeDataString(objecttypeUrl.ToString()) +
            "&data_attrs=id__exact__" + Uri.EscapeDataString(id));
        var page = await GetAsync<ObjectPage>(query, options.Token, crs: true, "objects", ct);
        var match = (page.Results ?? []).FirstOrDefault();
        return match is null ? null : new Uri(match.Url);
    }

    private async Task<T> GetAsync<T>(Uri uri, string token, bool crs, string label, CancellationToken ct)
    {
        using var message = new HttpRequestMessage(HttpMethod.Get, uri);
        message.Headers.Authorization = new AuthenticationHeaderValue("Token", token);
        if (crs)
            message.Headers.Add("Accept-Crs", "EPSG:4326");

        using var response = await http.SendAsync(message, ct);
        await EnsureSuccessAsync(response, $"Querying {label}", ct);

        return await response.Content.ReadFromJsonAsync<T>(ct)
            ?? throw new InvalidOperationException($"Objecten returned an empty {label} response");
    }

    private async Task SendAsync(HttpMethod method, Uri uri, object dto, string action, CancellationToken ct)
    {
        using var message = new HttpRequestMessage(method, uri) { Content = JsonContent.Create(dto) };
        message.Headers.Authorization = new AuthenticationHeaderValue("Token", options.Token);
        // The Objecten API is a geo API: it requires the CRS headers on reads and writes alike.
        message.Headers.Add("Accept-Crs", "EPSG:4326");
        message.Content.Headers.Add("Content-Crs", "EPSG:4326");
        // As with OpenZaak, Objecten runs behind uwsgi, which rejects a chunked request body.
        await message.Content.LoadIntoBufferAsync(ct);

        using var response = await http.SendAsync(message, ct);
        await EnsureSuccessAsync(response, action, ct);
    }

    // As in OpenZaakGateway: EnsureSuccessStatusCode discards the body, and the JSON validation error
    // Objecten returns on a schema mismatch is exactly what you need to diagnose a rejected write.
    private static async Task EnsureSuccessAsync(HttpResponseMessage response, string action, CancellationToken ct)
    {
        if (response.IsSuccessStatusCode)
            return;

        var body = await response.Content.ReadAsStringAsync(ct);
        throw new HttpRequestException($"{action} failed: {(int)response.StatusCode} {response.ReasonPhrase}. {body}");
    }

    private sealed record Objecttype(Uri Url, int Version);

    private sealed record ObjecttypePage(
        [property: JsonPropertyName("results")] IReadOnlyList<ObjecttypeDto>? Results);

    private sealed record ObjecttypeDto(
        [property: JsonPropertyName("url")] string Url,
        [property: JsonPropertyName("name")] string? Name,
        [property: JsonPropertyName("versions")] IReadOnlyList<string>? Versions);

    private sealed record ObjecttypeVersionDto(
        [property: JsonPropertyName("version")] int Version,
        [property: JsonPropertyName("status")] string? Status);

    private sealed record ObjectPage(
        [property: JsonPropertyName("results")] IReadOnlyList<ObjectDto>? Results);

    private sealed record ObjectDto(
        [property: JsonPropertyName("url")] string Url);

    private sealed record ReadObjectDto(
        [property: JsonPropertyName("record")] ReadRecordDto? Record);

    private sealed record ReadRecordDto(
        [property: JsonPropertyName("data")] RecordDataDto? Data);

    private sealed record CreateObjectDto(
        [property: JsonPropertyName("type")] string Type,
        [property: JsonPropertyName("record")] RecordDto Record);

    private sealed record PatchObjectDto(
        [property: JsonPropertyName("record")] RecordDto Record);

    private sealed record RecordDto(
        [property: JsonPropertyName("typeVersion")] int TypeVersion,
        [property: JsonPropertyName("data")] RecordDataDto Data,
        [property: JsonPropertyName("startAt")] string StartAt);

    private sealed record RecordDataDto(
        [property: JsonPropertyName("id")] string Id,
        [property: JsonPropertyName("status")] string Status,
        [property: JsonPropertyName("reference")] string? Reference);
}